Traditional first-step slurries for polishing nickel phosphorus (NiP) surfaces in rigid disk manufacturer typically contain alumina or mixture of alumina and colloidal silica as abrasive. Due to its high hardness, alumina can become embedded or partially embedded in the surface of the NiP substrate during polishing to form a defect. Such a defect may become a surface protrusion upon thermal treatment in subsequent processing steps in rigid disk manufacturing, resulting in a risk of magnetic head crashing when the head travels over the protrusion during the magnetic recording and reading process.
In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents, acids, bases, or other additives present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typically, first-step NiP polishing slurries utilize an oxidizing agent such as hydrogen peroxide to aid in removal of NiP.
In order to address and ameliorate the risk of head crash due to embedded alumina, there is a need to develop alumina-free polishing slurries for CMP of NiP. Slurries with colloidal silica alone as abrasive have been explored as one solution. However, in order to improve manufacturing throughput for cost of ownership (CoO) reduction, high removal rate continues to be one of the top requirements for slurries with silica only as abrasive. The compositions and methods described herein address this need by using fused silica as part of the abrasive package.